Stent delivery apparatus and method

ABSTRACT

A constrained stet has a plurality of stent retaining bands disposed about the stent which maintains the stent in a reduced diameter configuration. The stent is capable of being expanded from a reduced diameter configuration to a fully expanded configuration.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application from application Ser. No.09/369,918, filed Aug. 6, 1999, pending, which is a continuationapplication of application Ser. No. 08/633,726, filed Jun. 18, 1997, nowU.S. Pat. No. 5,985,280, which is a continuation-in-part of applicationSer. No. 08/141,269, filed Oct. 22, 1993 now U.S. Pat. No. 5,571,135 anda continuation-in-part of application Ser. No. 08/245,919, filed May 19,1994, now U.S. Pat. No. 5,445,646, the contents of each of which arehereby incorporated by reference

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a delivery system and method fordelivering and deploying a stent. More specifically, the inventionrelates to a delivery system and method for delivering and deploying aself-expanding stent in a body lumen.

2. Description of the Related Art

Stents and delivery systems for deploying stents are a highly developedand well known field of medical technology. Stents have many well knownuses and applications. A stent is a prosthesis which is generallytubular and which is expanded radially in a vessel or lumen to maintainits patency. Stents are widely used in body vessels, body canals, ductsor other body lumens.

The preferred present stent delivery apparatus and method utilizes aself-expanding stent, which is well known in the art. A well knownself-expanding stent is the woven braided stent disclosed in U.S. Pat.No. 4,655,771 (Wallsten); U.S. Pat. No. 4,954,126 (Wallsten) and U.S.Pat. No. 5,061,275 (Wallsten), although any type of self-expanding stentmay be deployed using the inventive delivery system and method. Thedelivery system of the present invention may also be used to deliver aballoon expanded stent and may also deliver stent grafts, which are wellknown in the art.

The delivery systems for stents are generally comprised of catheterswith the stent axially surrounding the distal end of the catheter. It ishighly desirable to keep the profile of the catheter as small aspossible. Therefore, self-expanding stents are generally confined in areduced radius for delivery to the deployment site. Once the stent isdeployed the catheter is removed, leaving the stent implanted at thedesired location to keep the vessel walls from closing.

A variety of techniques have been developed for holding a self-expandingstent in its reduced configuration while moving the distal end of thecatheter to the deployment site. For example, in U.S. Pat. No. 4,655,771(Wallsten), gripping members at either end of the stent hold the stentin an axially-elongated position, which causes the stent to take areduced radius delivery configuration.

Another common technique for maintaining the self-expanding stent in areduced radius delivery configuration is using a sheath which surroundsthe stent and compresses it around the catheter. This technique isdisclosed in U.S. Pat. No. 5,071,407 (Termin) and U.S. Pat. No.5,064,435 (Porter), both of which use a silicon rubber sheath tocompress the stent. A similar technique is disclosed in U.S. Pat. No.5,026,377 (Burton) and U.S. Pat. No. 5,078,720 (Burton).

A variation on surrounding the stent with a sheath is disclosed in U.S.Pat. No. 4,732,152 (Wallsten); U.S. Pat. No. 4,848,343 (Wallsten) andU.S. Pat. No. 4,875,480 (Imbert), all of which disclose using a sleeveformed of a doubled-over section of membrane to compress and contain thestent.

U.S. Pat. No. 5,234,457 discloses using a sheath to surround a meshstent of the type disclosed in U.S. Pat. No. 4,922,405. However, in thispatent the sheath is not used to compress the stent, but is used toprevent fluid from accessing the stent. The stent is impregnated with apure gelatin or other dissolvable material which, when cured, hassufficient strength to hold the stent in its reduced deliveryconfiguration. Once the sheath is withdrawn, the stent is exposed to thebody fluids which dissolve the gelatin, allowing the stent toself-expand. This reference also discloses using axial distribution ofgelatins with different rates of thermal decomposition to control thephysical profile of the stent as it expands. However, using animpregnated mesh stent adds several inconvenient manufacturing steps tothe process of preparing the stent for implantation.

All of the methods for delivery of a stent discussed to this pointinvolve releasing the stent starting from one end of the stent, exceptfor Anderson U.S. Pat. No. 5,234,457 which can allow the stent toself-expand uniformly over its entire length. An improvement to thistype of deployment is discussed in Heyn U.S. Pat. No. 5,201,757 whichrelates to medial deployment of a stent. Medial deployment of a stentreleases the middle region of the stent before releasing either end ofit. This tends to prevent stent movement during deployment.

All of the prior art methods of containing and deploying theself-expanding stent have several problems. First, many of thetechniques require that movement of the entire sheath or exteriorcatheter take place to manipulate the distal end of the catheter andeffect release of the stent. This can be seen in Wallsten U.S. Pat. No.4,655,771 and Wallsten U.S. Pat. No. 4,954,126 in which tubular member23 is moved forward from position 22 to position 30. In Termin U.S. Pat.No. 5,071,407 the sheath 32 is withdrawn proximally with respect to thestent. In Porter U.S. Pat. No. 5,064,435 the sheath 38 is withdrawnproximally with respect to the stent. Burton U.S. Pat. No. 5,026,377also moves an outer sleeve backwards relative to the stent. In WallstenU.S. Pat. No. 4,732,152; Wallsten U.S. Pat. No. 4,848,343, and ImbertU.S. Pat. No. 4,875,480, a hose 5 is connected to a maneuvering tube 8which runs the length of the catheter. Finally, in Heyn, finger grip 5,connected to section 58 causes outer catheter 20 and sleeve 24 to moveproximally relative to the stent.

In all of the cases discussed above, movement occurs over the entirelength of the catheter between the proximal end controlled by thephysician and the distal end where the stent is released. This cathetermovement in the vessel creates several problems. First, cathetermovement can disturb or move the introducer sheath at the wound sitewhere the catheter is inserted into the vessel. Secondly, in tortuousanatomy the added friction caused by rubbing the outer catheter againstthe vessel, as well as the added friction created between theinner/outer layer interface, can make deployment difficult. Thetranslation of control movements from the proximal to the distal end isimprecise, jerky and in some instances impossible due to the increasedfriction caused by tortuosity. Thirdly, it can create trauma to theendothelium over the entire length of the catheter.

Another drawback to the prior art stent delivery systems discussed aboveis that requiring an extra sheath layer, sleeve layer or layeredcatheters (Heyn) increases the profile of the catheter, which isundesirable. The Heyn device described in U.S. Pat. No. 5,201,757 has aprofile of 0.12 inches (3.048 mm). A reduction in profile of even 1F(French) is considered significant to those skilled in the art.

There remains a need in the art for a stent delivery system in which thecatheter remains stationary in the vessel and movement is confined tothe distal end of the catheter to avoid disturbing the introducersheath, minimize trauma to the endothelium and allow for easier and moreaccurate deployment in tortuous anatomy. Furthermore, there remains theneed for a stent delivery catheter with a smaller profile than the priorart. There is also a need for an improved form of medial release.

SUMMARY OF THE INVENTION

The inventive stent delivery device includes a catheter with a stentheld in a reduced delivery configuration for insertion and transportthrough a body lumen to a predetermined site for deployment of a stent,self-expanding stent, stent graft or the like. An embodiment utilizes apair of slipping sleeves, each being a section of membrane folded overonto itself, which can either hold a self-expanding stent in thedelivery configuration or form a watertight chamber for an enclosedholding means. When the slipping sleeves are used to form a watertightchamber, the stent is held in the delivery configuration by means of atubular sleeve made of water soluble material; a plurality of bands madeof water soluble material, swelling band(s) or other degradablematerial. A related embodiment can utilize only a single slipping sleevein a non-medial release form.

An alternate embodiment of the stent delivery device includes separatelumens, each containing a teflon or hydrophilic coated wire extending torespective proximal and distal movable sleeves. The physician canindividually control each sleeve by pulling on the wire connected to theproximal sleeve and/or pushing on the wire connected to the distalsleeve. A related embodiment can utilize only a single sleeve in anon-medial release form with a single wire.

In another embodiment of the stent delivery device, the separate lumenseach contain proximal and distal pistons which are connected by teflonor hydrophilic coated wires extending to their respective proximal anddistal sleeves. The lumens are connected by a fluid communication port,which is positioned such that the distal piston must move distally apredetermined distance before the fluid can access the port and flowinto the proximal piston lumen, where it moves the proximal pistonproximally. This causes a form of medial release in which the distalsleeve releases the distal end of the stent prior to release of theproximal end.

This application also discloses another embodiment called the singlelayer sheath stent delivery apparatus and method, which is animprovement of applicant's co-pending improved stent delivery apparatusand method application, filed Oct. 22, 1993 as Ser. No. 08/141,269, U.S.Pat. No. 5,571,135. The entire contents of Ser. No. 08/141,269 filedOct. 22, 1993 are hereby incorporated by reference.

The inventive single layer sheath stent delivery device embodimentincludes a catheter with a stent held in a reduced deliveryconfiguration for insertion and transport through a body lumen to apredetermined site for deployment of a stent, self-expanding stent,stent graft or the like. This embodiment utilizes a slipping sleeve,which is a section of membrane folded over onto itself, with a singlelayer sheath attached to the slipping sleeve which can hold aself-expanding stent in the delivery configuration. Fluid is insertedinto the slipping sleeve through a fluid access port, and the pressurecauses the slip seal end of the slipping sleeve to move axially awayfrom the stent, retracting the single layer sheath attached to theslipping sleeve, thereby releasing the stent to self-expand. Theinvention will also deliver non self-expanding stents by placing thestent around an expandable balloon. Once the single layer sheath isretracted, the balloon is expanded to expand the stent.

An alternate embodiment of the single layer sheath stent delivery deviceprovides medial release by using two single layer sheaths to retain thestent in the delivery configuration, each being attached to a slippingsleeve. Fluid pressure causes both slipping sleeves to move axially awayfrom the stent, retracting their respective sections of single layersheath to release the stent for self-expansion or balloon expansion.

Another alternate embodiment of the invention is a delivery system forimplantation of a stent in a vessel, which includes an elongate flexiblecatheter having proximal and distal ends for delivering a self-expandingstent to a predetermined location in a vessel, the self-expanding stenthaving proximal and distal ends, the stent being in a deliveryconfiguration where the stent has a reduced radius along its entireaxial length and where the stent is held in its reduced deliveryconfiguration by a swelling band stent retaining and release means forretaining the stent in the delivery configuration and for deploying thestent, comprised of at least one band made of a water swelling material,which holds the self-expanding stent in its delivery configurationagainst the outwardly urging force of the self-expanding stent untilfluid swells the band, thereby releasing the stent to self-expand.

BRIEF DESCRIPTION OF THE DRAWINGS

A detailed description of the invention is hereafter described withspecific reference being made to the drawings in which:

FIG. 1 is a side elevational section showing a stent deployment devicewith the slipping sleeves shown with the stent in the uncoveredposition, and with the stent held in a confined or reduced deliveryconfiguration with a plurality of water soluble bands;

FIG. 1A is a cross-sectional view of the stent deployment device of FIG.1 line 1 a— 1 a.

FIG. 1B is a cross-sectional view of the stent deployment device of FIG.1 along, line 1 b—1 b.

FIG. 1C is a cross-sectional view of the stent deployment device of FIG.1 along line 1 c—1 c.

FIG. 1D is a cross-sectional view of the stent deployment device of FIG.1 of FIG.1 along line 1 d— 1 d.

FIG. 2 is a side elevational section fragment of FIG. 2 showing the,slipping sleeves of FIG. 1 in the covered position;

FIG. 2A is a fragment of FIG. 2 showing an alternate embodiment of theslipping sleeve inflation of FIG. 2;

FIG. 2B is a fragment of FIG. 2 showing an alternate L-seal embodimentof the slipping sleeve;

FIG. 3 is a side elevational section of the distal end portion of adeployment device showing the slipping sleeves of FIG. 2 retracted andwith the middle bands dissolved;

FIG. 4 is a showing similar to FIG. 3 illustrating a first alternateembodiment of the water soluble bands of the invention;

FIG. 5 is a showing similar to FIG. 3 illustrating a second alternateembodiment of the water soluble bands of the invention;

FIG. 6 is a side elevational section showing another embodiment of astent delivery device according to the invention;

FIG. 7 is a side elevational section showing yet another embodiment of astent delivery device of the invention in an uncovered position;

FIG. 8 is a side elevational section of the distal end portion of theinvention of FIG. 7 in the covered position;

FIG. 8A is a fragment of FIG. 8 showing an alternate embodiment tosecure the slipping sleeve;

FIG. 9 is a side elevational section of the distal end portion of theinvention of FIG. 7 in mid-deployment;

FIGS. 10a and 10 b are side elevational sections of the distal endportion of the invention showing the use of a guide catheter to retrievea misplaced stent;

FIG. 11 is a side elevational section of a further embodiment of a stentdelivery device according to the invention;

FIG. 11A is a cross-sectional view of the stent deployment device ofFIG. 11 along line 11 a— 11 a.

FIG. 11B is a cross-sectional view of the stent deployment device ofFIG. 11 a long line 11 b— 11 b.

FIG. 12 is a side elevational section of a further embodiment of a stentdelivery device utilizing pistons and showing the position of thepistons when the stent is in the confined position;

FIG. 13 is a side elevational section of the embodiment of FIG. 12showing the position of the pistons when in the deployed position;

FIG. 14 is a side elevational section of the distal end portion of theembodiments of FIGS. 11 or 12, i.e., a push/pull version or a pistonoperated version, respectively, the stent being in the confinedposition;

FIG. 15 is a side elevational section of the distal end portion of theembodiments of FIGS. 11 or 12, the stent being in the deployed position;

FIG. 16 is a side elevational section showing a single layer sheathalternate embodiment;

FIG. 17 is a side elevational section showing another embodiment of thesingle layer sheath stent delivery device, and

FIG. 18 shows yet another embodiment of the inventive stent deliverydevice.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

While this invention may be embodied in many different forms, there areshown in the drawings and described in detail herein specific preferredembodiments of the invention. The present disclosure is anexemplification of the principles of the invention and is not intendedto limit the invention to the particular embodiments illustrated.

FIG. 1 shows an embodiment of the inventive stent delivery apparatus,generally at 10, which is used to deliver the stent in a reduced radiusdelivery configuration to the deployment site in the body. Apparatus 10includes an elongate flexible catheter 12, which in the this embodimentis extruded of a biocompatible and HPC (hydrophilic) compatible materialsuch as a lubricous polyimide or polyethylene. Other suitable materialsfor catheter 12 include nylons, urethanes, polypropylene, and PEBAXmaterials which are compatible with silicone and/or hydrophiliccoatings. It should be understood that while a hydrophilic compatiblematerial is preferred, any biocompatible material may be used. Thepolyethylene or polypropylene, while not themselves hydrophilic can becoated with a hydrophilic material. Therefore, it can be seen that anybiocompatible or HPC compatible material can be used to make catheter12. As will be discussed below, the inventive stent delivery apparatusallows for the outside diameter of the catheter to be 5.3 French (F)(0.070 inches or 1.778 mm) or less using a 0.018 inch guidewire, whichis a significant profile improvement over prior art such as Heyn U.S.Pat. No. 5,201,757 which discloses an outer diameter of 0.12 inches(3.048 mm).

The distal end portion of catheter 12 has a pair of slipping sleeves 14and 16 which are used to form a waterproof chamber around a stent 17carried by the catheter. Although this invention will be relatedprimarily to using the inventive delivery apparatus for delivery ofself-expanding stents, it should be understood that the inventivedelivery apparatus may be used to deliver both self-expanding and nonself-expanding stents, grafts and stent grafts. Stent 17 is aself-expanding stent, and in this embodiment is a so called wovenbraided stent of a type somewhat similar to those disclosed in WallstenU.S. Pat. No. 4,655,771; Wallsten U.S. Pat. No. 4,954,126 and WallstenU.S. Pat. No. 5,061,275. However, the disclosed stent delivery apparatuswill deliver any type of self-expanding stent, such as for example, astent made of any type of resilient metal or plastic, which wouldinclude a shape memory alloy type stent, such as a nitinol stent. Stent17 is shown confined in its reduced radius delivery configuration by aplurality of water soluble bands 18, described further hereinbelow inFIGS. 3-6. Two pair of radiopaque marker bands 20 and 22 are bonded tocatheter 12 with the marker bands of pair 20 being enlarged in diameterso as to additionally be used to aid in preventing stent 17 from movingaxially while on the catheter. The use of radiographic or fluoroscopicimaging techniques to image the radiopaque marker bands to verify thecorrect positioning for stent deployment is well known in the art.

Slipping sleeves 14 and 16 are shown in FIG. 1 in the uncoveredposition. The slipping sleeves 14 and 16 are made of molded plastic andthe preferred material is a polyolefin copolymer (POC) SURLYN™. Othermaterials such as fluoropolymers, noncompliant polyethyleneterephthalate (PET); polyimide, nylon, polyethylene, PEBAX or the likemay also be used. In this embodiment, slipping sleeves 14 and 16 aremolded with an approximately 90° knee, shown at 24, and an approximatelya 45° angle at 26. It has been found experimentally that the 90° knee at24 and the 45° angle at 26 more easily allow the sleeve membranematerial to roll over onto itself. Slipping sleeves 14 and 16 are slidover the catheter and bonded to the catheter at 28, as is well known inthe art. The slipping seal 30 is formed a tolerance fit between theinner diameter of the seal 30 and the outer diameter of the cathetershaft.

A potential problem with a tolerance fit seal design is encountered whenthe slipping sleeve is restricted and a great deal of pressure isrequired to slide the sleeve. In this case, the pressure can becomegreat enough to separate the seal and allow fluid to leak between theinner diameter of the seal 30 and the outer diameter of the cathetershaft. In seal design theory, it is a goal to have the integrity of theseal increase as pressure is increased. An embodiment that does this isshown in FIG. 2B by adding member 25. Member 25 is glued to the innerdiameter of the sleeve and has a length protruding under the sleeve, andis therefore called an “L seal”. As pressure is increased in theballoon, the L seal is held more tightly against the outer diameter ofthe catheter, decreasing the possibility of fluid leakage allowingpressure to build and slide the sleeve.

Manifolds 44 and 46 are used to introduce fluid into lumens 32 and 34respectively. Manifold 48 is used to insert a guide wire 50 throughcentral lumen 52, as is well known in the art. The catheter can beinserted into a wound and into a vessel through the use of an introducersheath.

One advantage the inventive stent delivery apparatus provides is thatonce the catheter has reached the deployment site, no further movementof the catheter is required to release the stent. All movement requiredto release the stent is internal to the catheter. By avoiding farthermovement of the catheter 12, an introducer sheath is not disturbed ormoved from its body introduction site, which reduces trauma to theentrance wound. Also, avoiding further movement of catheter 12 minimizestrauma to the endothelium, which is desirable. By avoiding externalcatheter movement to deploy the stent 17, the inventive deliveryapparatus can be used to deliver stents in more tortuous anatomy as wellas allow more precise and accurate control.

Referring now to FIG. 2, the distal end portion of catheter 12 is shownwith slipping sleeves 14 and 16 forming a waterproof chamber aroundstent 17. Slipping sleeves 14 and 16 are formed of a doubled-oversection of membrane caused by urging seals 30 of sleeves 14 and 16axially toward each other. This causes the membranes to roll over fromtheir position as seen in FIG. 1 onto themselves at knees 24 as is seenin FIG. 2. It can be seen that sleeves 14 and 16 slightly overlap toform a seal. Stent 17 confined to its reduced radius by bands 18 andpositioned between marker bands 20 in the chamber formed by sleeves 14and 16.

FIG. 3 shows the apparatus of FIGS. 1 and 2 in mid-deployment, i.e. thetwo center bands being dissolved Fluid has been introduced throughmanifolds 44 and 46 and into lumens 32 and 34 to enter sleeves 14 and16. The chamber formed by the sealed end 28 and the slipping seal 30 ofthe sleeve is filled through inflation ports 36 and 38 of each sleeve,respectively. As the fluid pressure builds in sleeves 14 and 16, fluidis forced out through seal 30 causing seal 30 to slide away from thestent 17 along the catheter 12, thereby retracting sleeves 14 and 16 toexpose or uncover stent 17 to body fluids.

The water soluble bands 18 are preferably a polyethyleneoxide (PEO), butcan be polyvinylpryyolidone (PVP); polyvinyl alcohol (PVA); mannitol,complex carbohydrates or the like, and the composition of individualbands can be varied as desired. In FIG. 3, the bands surrounding themedial portion of stent 17 were constructed such that they dissolvedfaster than the outer bands 18, resulting in the medial release shown inFIG. 3. This can be accomplished by varying the molecular weights of thecompositions, since the lower the molecular weight the faster the band18 will dissolve. Varying the thickness or adding perforations(discussed below in connection with FIGS. 5 and 6) will also increasethe rate of dissolution.

FIGS. 4 and 5 show alternate embodiments of water soluble bands 18. InFIG. 4, the plurality of bands axially spaced along stent 17 as shown inFIG. 2 have been replaced by a single tubular band 60. In the embodimentof tubular band 60 shown in FIG. 4, the band is thinner in the middlethan at either end and will therefore dissolve faster in the middle,allowing medial deployment. It can be understood that the thickness ofband 60 can be varied as desired to allow for a controlled release ofstent 17 in any manner desired by the physician, such as releasing thestent starting from either the proximal or distal end or in othersequential deployments. It should also be understood that band 60 can beof the same thickness, but by varying the composition of predeterminedsections of the band 60, those predetermined sections can be dissolvedat a faster rate, allowing for a controlled release of stent 17.

FIG. 5 shows a tubular band 62 which has perforations 64 throughout.Perforations 64 are more dense in the middle section of band 62 than ateither end section, thereby allowing the middle section of band 62 todissolve faster, whether composition or thickness is varied or both.Again, the denseness of perforations 64 can be controlled throughoutband 62 to allow for any type of sequential dissolution andself-expansion of stent 17, as desired.

An alternate embodiment to the use of water soluble bands 18, 60 or 62is to utilize a swelling band or other degradable material which isattached to the catheter 12. This swelling band material can be complexcarbohydrates, cellulose, crosslinked PVA/PVP, polyethylene/acrylic acidor the like. Self-expanding stent 17 is pressed into the swelling bandmaterial, which after curing, will hold stent 17 in its reduced radiusdelivery configuration. Retracting sleeves 14 and 16 exposes theswelling band material to body fluids, which will expand or swell,releasing the stent 17 to self-expand. Because the swelling bandmaterial is attached to the catheter 12, it will be withdrawn from thebody along with the catheter. It should be understood that thecomposition of the swelling material could be varied to control theexpansion of stent 17 as above.

FIG. 6 shows another embodiment of the stent delivery device in whichthe sleeves 14 and 16 have been replaced by a retractable sheath 66.Retractable sheath 66 can be withdrawn using a wire as discussed belowin connection with the push/pull sleeve and hydraulic sleeveembodiments. Retraction of sheath 66 allows body fluid to access anddissolve band 60. It should be understood that the variations of watersoluble or swelling material described above can be used in connectionwith this embodiment.

One of the important features of the inventive stent delivery apparatusis that it allows the physician to deploy the stent in a variety ofways. For example the stent can be medially deployed, deployed startingfrom the distal end of the stent or deployed starting from the proximalend of the stent. With medial deployment, either the proximal or distalend of the stent can be released from its sleeve first or they can bothbe released at the same time, which provides maximum flexibility to thephysician.

This deployment flexibility can be accomplished in several ways. Oneversion shown in FIG. 1 is the use of separate lumens 32 and 34 forinflating slipping sleeves 14 and 16, through inflation ports 36 and 38,to allow individual control over each sleeve 14 and 16. This is bestseen in FIG. 2. Another version is shown best in FIG. 2A, where both theproximal inflation port 36 and the distal inflation port 38 share thesame lumen, which allows for a decreased profile. In the shared lumenversion, there are several ways to control the movement of sleeves 14and 16. Sleeves 14 and 16 can be sized differently, as shown in FIG. 1,such that equal sleeve inflation will cause the distal sleeve 16 torelease the distal end of stent 17 before the proximal end of stent 17is released by the proximal sleeve 14. The tightness of seal 30 of eachsleeve can be varied as well by controlling the immersion time andtemperature in the hot water bath. Also, speed control bumps 42 orridges can be formed in the catheter 12 (best shown in FIG. 3) toindividually control the slipping of each sleeve 14 and 16. The sleeveouter diameter could also be varied, which would vary the movement ofthe slipping sleeves. Of course, all of the various techniques could beeasily combined as well by those skilled in the art.

It should also be noted that although preferred, the water soluble bandsare not required in the embodiment of FIG. 1. Sleeves 14 and 16 canoptionally be used to contain stent 17 as disclosed in Wallsten U.S.Pat. No. 4,732,152; Wallsten U.S. Pat. No. 4,848,343 and Imbert U.S.Pat. No. 4,875,480. The same means used to cause sleeves 14 and 16 toretract will also permit the stent to self-expand as sleeves 14 and 16are retracted. It should also be understood that the various techniquesof varying the sleeve lengths of sleeves 14 and 16, the tightness of theslipping seal 30, the outside diameter of sleeves 14 and 16, placementof speed control bumps 42 on catheter 12 and individual lumens for eachof the sleeves 14 and 16 allow for great control over the movement ofsleeves 14 and 16, with or without water soluble band(s) 18, 60 or 62.

Referring now to FIGS. 7-10, yet another embodiment of the stentdelivery device is shown in which a single slipping sleeve 70 is shownin the uncovered position (FIG. 7). The distal end of sleeve 70 iscontained by cylindrical gripping means 72, which is made of siliconerubber, latex or the like, and is bonded to catheter 12 with an open endoriented toward the sleeve and the stent to receive them as best seen inFIG. 8. The stent 17 may, but need not, extend into gripping means 72along with sleeve 70. FIG. 8 shows the device in the covered positionwith the stent 17 confined to its reduced radius delivery configuration.It should be understood that this embodiment, like those disclosed abovecan optionally use water soluble band(s) 18, 60, 62, a swelling materialor other degradable material to confine stent 17, or stent 17 can beheld in its reduced delivery configuration by sleeve 70 alone.

An alternate embodiment of the invention of FIGS. 7-10 replaces thecylindrical gripping means 72 with the embodiment shown in FIG. 8A. Inthis case the gripping means 72 has been replaced with a silicon ball 73that allows the sleeve to be rolled over it to create a water tightseal. Other materials and shapes can be used that have a desired degreeof compliance with the slipping sleeve.

FIG. 9 shows the device in mid-deployment. Retraction of sleeve 70 haspulled stent 17 from gripping means 72 and allowed stent 17 toself-expand as shown.

FIGS. 10A and 10B show a technique for recovering a misplaced stentprior to completely releasing the stent shown in FIG. 9. A guidecatheter or other tubular sheath 76 is advanced to surround sleeve 70and partially deployed stent 17, then the entire assembly is withdrawnfrom the body lumen.

Referring now to FIG. 11, another embodiment of a stent delivery deviceis shown which uses push/pull wires to move a pair of sleeves. Catheter12 can be seen to have three lumens in sectioned view 11A, a centerlumen 52 for guide wire 50, a proximal lumen 80 for proximal pull wire82 and a distal lumen 84 for distal push wire 86. Sectioned view 11Bshows that the catheter has a skived cross-section to allow proximalwire 82 to leave the lumen and to attach to proximal sleeve 88. Distalwire 86 leaves its lumen and attaches to distal sleeve 90 at 92. Byappropriately pushing on a handle 93 attached to distal push wire 86,and pulling on a handle 95 attached to proximal pull wire 82, thephysician can release stent 17. This arrangement also allows controlover which end of the stent is released first. Both wires 82 and 86 maybe teflon coated to lessen the friction caused by movement in theirrespective lumens.

Referring now to FIGS. 12 and 13, another embodiment of a stent deliverydevice is shown which uses hydraulic pressure to move a pair of sleeves.FIG. 12 shows catheter 12 proximally of the distal end with a distalpiston 90 in lumen 92 and a proximal piston 94 in lumen 96. Wires 98 and100 extend from the pistons 90 and 94, respectively, to attach to thesleeves 90 and 88 as in the previous embodiment. Wire 100 extendsthrough a fixed seal 102. FIG. 13 shows this embodiment in the deployedposition, where fluid pressure in lumen 92 has pushed distal pistondistally, thereby pushing distal sleeve 90 distally. Once distal pistonis past access port 104 the fluid will enter lumen 96 and force proximalpiston proximally in lumen 96, thereby pulling proximal sleeve 88proximally.

FIGS. 14 and 15 show the distal end of the catheter for both theprevious two embodiments in both the confined and deployed positions.Catheter securing balloons 106 can be optionally inflated prior todeployment to aid in preventing catheter movement during deployment byfrictionally engaging vessel wall 108. Balloons 106 are made from a morecompliant material such as latex, silicone or the like, and are wellknown in the art. Catheter securing balloons 106 can be used inconnection with any of the embodiments by simply adding the appropriatelumens or access from existing fluid lumens. The catheter can also besecured in the vessel by means of a magnet attached to the proximal endportion of the catheter and guidewire, with the guidewire secured usinga magnet external of the body.

Once the stent is deployed using any of the embodiments, a placementballoon 110 (best seen in FIG. 9) can be inflated to seat the stent intothe vessel wall, as is well known in the art. It should be understoodthat the placement balloon, as well as a partially deployed stent, ifdesired, can be recovered using the push/pull wire embodiment. For theother embodiments, if necessary a guide catheter or sheath can beadvanced to retrieve the placement balloon or partially deployed stents.

It has been found that delivering an uncovered stent to a deploymentsite can damage the vessel wall, due to the sharp edges of the stent. Ithas also been found that an uncovered stent may move axially along thecatheter and may even slide off the catheter. Therefore the inventivedelivery system can also advantageously be used to deliver a nonself-expanding stent to a deployment site safely since the stent iscovered and prevents movement of the stent, relative to the catheter,before deployment. A non self-expanding stent can be deployed by using aplacement balloon of the type shown in FIG. 9 (reference 110) to expandstent 17, as is well known in the art.

Referring now to FIG. 16, a single layer sheath embodiment of the stentdelivery device is shown in which reference numeral 32 is a fluid lumenfor providing fluid through fluid access port 200 to the slipping sleeve202. Adhesively attached to the slipping sleeve 202 is the single layersheath 204 which can retain the stent 17 in its delivery configuration.The stent is secured between stent bumper 206 and fluid tight seal 208.As fluid is pumped through lumen 32 into slipping sleeve 202, theslipping seal 30 moves axially away from the stent 17, retracting thesingle layer sheath 204 and allowing the stent 17 to self-expand. Stent17 may optionally be surrounded by a dissolving band or pressed into aswelling band, as discussed above, the band acting to restrain the stent17 in its delivery configuration. Retraction of the single layer sheath204 allows fluid access to the dissolving or swelling band, which allowsthe stent to self-expand in a controlled manner as discussed above. Thesingle layer sheath may be made from the same materials and in the samemanner as discussed above in connection with the slipping sleeves.

Referring now to FIG. 17, an alternate embodiment of the single layersheath stent delivery device is shown in which reference numeral 32 is ashared fluid lumen for providing fluid through fluid access ports 200and 201 to the slipping sleeves 202 and 203. Separate fluid lumens canalso be provided as in FIG. 1 to allow individual control over eachslipping sleeve. Adhesively attached to the slipping sleeves 202 and 203are the single layer sheaths 204 and 205 which can retain the stent 17in its delivery configuration. The stent 17 is secured between stentbumpers 206 and 207 and the single layer sheaths 204 and 205 may abut toprovide a fluid tight seal, if desired. As fluid is pumped through lumen32 into slipping sleeves 202 and 203, the slipping seals 30 move axiallyaway from the stent 17, retracting the single layer sheaths 204 and 205,allowing the stent 17 to self-expand. Stent 17 may optionally besurrounded by a dissolving band or pressed into a swelling band, asdiscussed above, the band acting to restrain the stent 17 in itsdelivery configuration. Retraction of the single layer sheaths 204 and205 allows fluid access to the dissolving or swelling band, which allowsthe stent to self-expand in a controlled manner as discussed above.

Applicants' have discovered experimentally that the 45° knee 26(discussed above) in the slipping sleeve is sometimes weakened due tothe forces acting on the 45° section of slip seal 30. Therefore, toprovide additional strength, the embodiments of FIGS. 16 or 17 may beformed with 90° knees 210, with the knee filled with a cone shapedadhesive ridge 212 shown in FIG. 17. The adhesive ridge 212 supports the90° knee 210 and provides a smooth 45° transition zone which more evenlytransfers the force to the slip seal 30.

Referring now to FIG. 18, an alternate embodiment of the invention isshown in which the self-expanding stent is any self-expanding stent madeof a resilient metal or plastic material, which would include shapememory metal stents such as nitinol stents, which are well known in theart. The self-expanding stent is retained in its reduced delivery radiususing a collagen sleeve, liner or both.

Applicants have a copending application entitled “IMPROVED TISSUESUPPORTING DEVICES” filed May 19, 1994 as Ser. No. 08/246,320 whichdiscloses a preferred stent. The entire contents of Ser. No. 08/246,320are hereby incorporated by reference. The stents described in thisapplication are generally cylindrical or tubular in overall shape and ofsuch a configuration as to allow radial expansion for enlargement.Furthermore, the stents are comprised of at least one component whichexhibits a resiliency or spring-like tendency to self-expand the deviceand at least one other component which is deformable so as to allow anexternal force, such as a balloon positioned within the body of thedevice, to further expand it to a final desired size. Preferably, thestents are made of metal and most preferably of shape memory alloys.

In its broader concept, the device, such as a stent of Ser. No.08/246,320 is made of a first component which is a resilient spring-likemetal for self-expansion and the second component is a deformable metalfor final sizing. In the more preferred shape memory embodiment, thefirst component is a self-expanding austenitic one and second is anmartensitic one capable of deformation.

The most preferred embodiment the device described in 08/246,320 is astent, preferably of shape memory alloy. The most preferred shape memoryalloy is Ni—Ti, although any of the other known shape memory alloys maybe used as well. Such other alloys include: Au—Cd, Cu—Zn, In—Ti,Cu—Zn—Al, Ti—Nb, Au—Cu—Zn, Cu—Zn—Sn, Cu—Zn—Si, Cu—Al—Ni, Ag—Cd, Cu—Sn,Cu—Zn—Ga, Ni—Al, Fe—Pt, U—Nb, Ti—Pd—Ni, Fe—Mn—Si, and the like. Thesealloys may also be doped with small amounts of other elements forvarious property modifications as may be desired and known in the art.

The stent used in connection with any of the embodiments describedherein is preferably the two component stent described above. However, atypical memory metal self-expanding stent, such as a nitinol stent, mayalso be used. Any type of self-expanding stent, whether made of aresilient metal or plastic material, may be used. The term nitinol isintended to refer to the two component memory metal stent discussedabove as well as any other type of known memory metal stent.

Applicants have found that in delivering a self-expanding stent, such asthe preferred two component nitinol stent described above, as the stentis moved through the body carried by the catheter, the body temperatureof the patient may heat the nitinol stent to its transition temperature,causing it to self-expand. This is considered undesirable because it canexert an outward force on the various sheaths discussed above inconnection with FIGS. 1-18 which prevent fluid from hydrating the stent.

It is also known to insert a stent at the proximal end of the catheter,and push the stent through a lumen inside the catheter and out thedistal end of the catheter at the deployment site. Such a device isdisclosed for example in European Patent Application EP 0 556 850 A1,published Aug. 25, 1993. As the stent is moving through the lumen of thecatheter, the body temperature of the patient may heat the nitinol stentto its transition temperature, causing it to self-expand. This canincrease the frictional engagement of the stent with the lumen of thecatheter, making it difficult to push down the length of the catheter tothe delivery site at the distal end.

Applicants overcome this problem by surrounding the stent with an outersleeve of water swelling material, such as collagen, lining the insideof the stent with a swelling material, or both. This alternateembodiment may be used in connection with the various embodimentsdiscussed above in connection with FIGS. 1-17 to eliminate the outwardself-expanding force exerted by an type of memory metal stent after ithas reached its transition temperature.

Referring now to FIG. 18, the water swelling sleeve and/or linerdiscussed above is shown in a stent pusher embodiment. The catheter isreferred to generally at 300 and the guidewire at 302. Theself-expanding stent, including its collagen sleeve, liner or both isshown generally at 304, axially surrounding the guidewire. Stent pusher306 is used to push the stent through the lumen of catheter 300 and outthe distal end of the catheter to the delivery site. In the preferredembodiment, the water swelling material is formulated so that it is slowto hydrate to allow sufficient time to deliver the stent to thedeployment site. Alternatively, a means could be included which wouldprevent the stent from being hydrated until the collagen sleeve and/orlined stent was delivered to its deployment site.

The stent can be surrounded by an outer sleeve of water swellingmaterial, which in this embodiment is preferably collagen. The stent canoptionally also be held in its reduced delivery configuration by a linerof collagen which is inside the stent. Finally, the stent can optionallyuse both the outer sleeve and the inner liner.

The collagen sleeve may be of collagen per se or it may be carried on asupport such as DACRON® fabric or the like as is known and disclosed forexample in U.S. Pat. Nos. 5,256,418, 5,201,764 and 5,197,977, the entirecontent of which are all incorporated herein by reference, particularlythose portions which relate to the formation of collagen tubes. Thesupport may be a fabric, woven or braided, and may also be of polyester,polyethylene, polyurethane or PTFE. The term “collagen material” is usedherein to refer to both supported and unsupported collagen for thesleeve element of this invention.

The preferred collagen at present appears to be intestinal collagenbelieved to be of Type I and Type IV, and in particular a collagen knownas Small Intestine Submucosa (SIS) which has particular use herein,alone and in combination with other collagen material such as Type I.SIS is predominantly a Type IV material. It is described in detail inU.S. Pat. Nos. 4,902,508; 4,956,178 and 5,281,422, all of which areincorporated herein by reference. In addition to SIS, with or withoutType I, the collagen may also be made of Type III or Type IV orcombinations thereof. U.S. Pat. Nos. 4,950,483, 5,110,064 and 5,024,841relate to collagen productions and are incorporated herein by reference.Collagen can be extracted from various structural tissues as is known inthe art and reformed into sheets or tubes and attached to a fullyexpanded stent, by for example, wrapping the stent with the collagen andattaching the collagen to itself or by weaving the collagen through theopenings in the stent and attaching it to itself. The stent is thenmechanically pulled down to its reduced diameter and the collagen isdried, which holds the stent in its reduced diameter. The collagen mayalso be dried onto the unexpanded stents mentioned above.

As such, stent sleeves and/or liners constructed of these materials canbe used for reservoirs for pharmaceutical agents and the like.Hydrophilic drugs such as heparin or hirudin to protect againstcoagulation or hydrophobic drugs such as prostaglandins or aspirin andvitamin E may be used to protect against platelet activation. Vitamin Eand other anti oxidants such as sodium ascorbate, phendies, carbazoles,and tocotrienols may be used to protect against oxidation. Mostpreferably, the collagen material will include a quantity of drugmaterial such as heparin which may be incorporated into the collagen inknown manner for release after placement of the stent. Generally, thedrug materials may include the known antithrombic agents, antibacterialand/or antimicrobial agents, antifungal agents and the like.

During the formation process of the sleeve or liner, various componentsmay be added to the solution prior to drying or may be added separatelyafter formation of the device. Heparin could be directly added to theforming solution as could aspirin. Benzalkonium heparin, a modified formof heparin which makes it more hydrophobic could be used to coat theformed device or film from a solution of alcohol. Prostaglandins PGI2 orPGE2 may be added from a solution of propanol or propanol/methylenechloride onto a collagen sleeve formed from an aqueous base. Vitamin Ecould be added from even less polar solutions as chloroform. Otheragents could be similarly added. The term “agents” is used herein toinclude all such additives.

Cells of the blood vessel wall synthesize and secrete several kinds ofmacromolecules forming extracellular matrix. The components of thismatrix comprise several large proteins that may be syntheticallyconstructed to form films, tubes or multilayer sheets or otherconstructs. Among these biological components are collagens of severaltypes, elastin, glycosaminoglycans (GAGS), fibronectin and laminin.Collagens are three chain glycoproteins with molecular weights of about300,000. Elastin is an insoluble nonpolar amino acid rich crosslinkedprotein. The GAGs are linear chain polysaccharides with various negativecharges with various molecular weights ranging from thousands tomillions. Included in the GAGs are heparin and heparin sulfate, dermatinsulfate and chondroitin sulfate. Fibronectin is a 440,000 MW 2-chainadhesive glycoprotein that acts as a substrate for many cell types andin cell-cell interactions. Laminin is a 2 chain glycoprotein of MW about850,000 and acts as a basement membrane structure for cellular-molecularinteractions. Each of these macromolecules may be combined in amultitude of combinations to form composites. These are all naturalmaterials that serve specific functions and are exposed to blood undernormal repair conditions. It is therefore expected that, if a coveringsleeve for a stent were made of these macromolecules and used in thecourse of intervention, repair of a blood vessel would proceed morenaturally than if a similar device were constructed of syntheticpolymers such as polyethylene, polyteraphthalate or polyurethanes.Macromolecules are also referred to herein generally as “collagen”. Inthis patent collagen thus refers to not only the specific class ofmacromolecules known as collagen but those natural materials thatnormally or naturally form membranes with collagen as laminin,glycosaminoglycans, proteoglycans, pure carbohydrates, fibrin,fibronectin, hyaluronic acid or the like, and other natural materialsthat come into contact with collagen that could be made into film asalbumin, globulins, and other blood borne proteins. Tubular films madefrom any combination of the above materials could provide substantiallythe same purpose as that of pure collagen.

The collagen sleeve/liner discussed above could also be used with theembodiments disclosed above in connection with FIGS. 1-17. For example,the retractable sheath 66 discussed above in connection with FIG. 6could prevent fluid access to the collagen material until a wire is usedto retract the sheath 66, allowing fluid to access the collagenmaterial, allowing it to swell.

It should also be understood, that the collagen material remains in thebody, whether as a sleeve surrounding the stent, a liner inside thestent or both, to aid forming of a non-thrombogenic cushion for thestent in the vascular lumen as well as a natural substrate forendotheliazation. It should also be understood that the dissolving bandembodiments discussed above could also be used as an alternative to theswelling band material such as collagen, but are not preferred sincethey do not remain behind as a non-thrombogenic agent.

This completes the description of the preferred and alternateembodiments of the invention. It is to be understood that even thoughnumerous characteristics and advantages of the present invention havebeen set forth in the foregoing description, together with the detailsof the structure and function of the invention, the disclosure isillustrative only and changes may be made in detail, especially inmatters of shape, size and arrangement of parts within the principals ofthe invention, to the full extent indicated by the broad, generalmeaning of the terms in which the appended claims are expressed. Thoseskilled in the art may recognize other equivalents to the specificembodiment described herein which are intended to be encompassed by theclaims attached hereto.

What is claimed is:
 1. A constrained stent comprising: a stentexpandable from a reduced diameter configuration to a fully expandedconfiguration, the stent having an outer surface and an inner surface; aplurality of stent retaining bands disposed about the stent, eachretaining band having an inner surface and an outer surface, the innersurface of the band disposed against the outer surface of the stent, thestent retaining bands maintaining the stent in the reduced diameterconfiguration.
 2. The constrained stent of claim 1 wherein the retainingbands are constructed and arranged so as to release the stent in apredetermined sequence.
 3. The constrained stent of claim 2 wherein thestent has a proximal portion, a distal portion and a middle portiondisposed between the proximal and distal portions, and the retainingbands are constructed and arranged to release the middle portion of thestent before the proximal and distal portions of the stent.
 4. Theconstrained stent of claim 2 wherein the plurality of retaining bandsincludes bands of different thicknesses.
 5. The constrained stent ofclaim 2 wherein the plurality of retaining bands includes bands ofdifferent compositions.
 6. The constrained stent of claim 1 wherein thestent is self expanding.
 7. The constrained stent of claim 1 wherein thestent is a balloon assisted expanding stent.
 8. The constrained stent ofclaim 1 further comprising a sleeve disposed about the exterior of thestent.
 9. The constrained stent of claim 1 further comprising a linerdisposed about the interior of the stent.
 10. The constrained stent ofclaim 1 wherein the retaining bands are a disposed about the exterior ofthe stent.
 11. A constrained stent comprising: a stent expandable from areduced diameter configuration to a fully expanded configuration, thestent having an outer surface and an inner surface; and at least onestent retaining band disposed about the stent, the retaining band havingan inner surface and an outer surface, the inner surface of the banddisposed against the outer surface of the stent, the stent retainingband maintaining the stent in the reduced diameter configuration whereinthe stent retaining band is made of a water soluble material selectedfrom the group consisting of PEO, PVP, PVA, mannitol and complexcarbohydrates.
 12. A constrained stent comprising: a stent expandablefrom a reduced diameter configuration to a fully expanded configuration;and at least one stent retaining band disposed about the stent, thestent retaining band maintaining the stent in the reduced diameterconfiguration wherein the at least one retaining band has perforationstherein.
 13. The constrained stent of claim 12 wherein the density ofperforations on the retaining band is varied along the retaining band ina predetermined way.
 14. A constrained stent comprising: a stentexpandable from a reduced diameter configuration to a fully expandedconfiguration, the stent having an outer surface and an inner surface;and at least one stent retaining band disposed about the stent, theretaining band having an inner surface and an outer surface, the innersurface of the band disposed against the outer surface of the stent, thestent retaining band maintaining the stent in the reduced diameterconfiguration wherein the composition of the band is varied inpredetermined sections.
 15. A constrained stent comprising: a stentexpandable from a reduced diameter configuration to a fully expandedconfiguration; a plurality of stent retaining bands disposed about thestent, the stent retaining bands maintaining the stent in the reduceddiameter configuration wherein the thickness of the retaining bands isvaried in predetermined sections of the bands.
 16. A constrained stentcomprising: a stent expandable from a reduced diameter configuration toa fully expanded configuration, the stent having an outer surface and aninner surface; and at least one stent retaining band disposed about thestent, the retaining band having an inner surface and an outer surface,the inner surface of the band disposed against the outer surface of thestent, the stent retaining band maintaining the stent in the reduceddiameter configuration, the band constructed and arranged so as to allowfor a controlled expansion of the stent wherein desired portions of thestent are released to expand in a desired sequence.
 17. The constrainedstent of claim 16 wherein the stent has a proximal portion, a distalportion and a middle portion disposed between the proximal and distalportions, the retaining band constructed and arranged to release themiddle portion of the stent before the proximal and distal portions ofthe stent.
 18. A constrained stent-graft comprising: a stent-graftexpandable from a reduced diameter configuration to a fully expandedconfiguration, the stent-graft having an outer surface and an innersurface; and at least one stent-graft retaining band disposed about thestent-graft, the retaining band having an inner surface and an outersurface, the inner surface of the band disposed against the outersurface of the stent,-graft, the stent-graft retaining band maintainingthe stent-graft in the reduced diameter configuration.
 19. Theconstrained stent-graft of claim 18 comprising a sleeve comprised ofcollagen.
 20. The constrained stent-graft of claim 19 wherein thecollagen is carried on a support.
 21. The constrained stent-graft ofclaim 20 wherein the support is a woven or braided fabric.
 22. Theconstrained stent-graft of claim 20 wherein the support is made from amaterial selected from the group consisting of polyester, polyethylene,polyurethane and PTFE.
 23. A prosthesis comprising: an expandableprosthesis expandable from a reduced diameter configuration to a fullyexpanded configuration, the expandable prosthesis having an outersurface and an inner surface, the expandable prosthesis characterized bya length; and at least one prosthesis retaining band disposed about theexpandable prosthesis, the retaining band having an inner surface and anouter surface, the inner surface of the band disposed against the outersurface of the prosthesis, the prosthesis retaining band characterizedby a length, wherein the length of the prosthesis retaining band is lessthan the length of the expandable prosthesis.
 24. The prosthesis ofclaim 23 wherein the expandable prosthesis is selected from the groupconsisting of self-expanding stents, balloon expandable stents, non-selfexpanding stents, grafts and stent grafts.
 25. The prosthesis of claim23 where the expandable prosthesis is a stent made from a materialselected from the group consisting of resilient metals, deformablemetals, shape memory metals and plastic.
 26. The prosthesis of claim 23wherein the retaining band maintains the expandable prosthesis in apartially expanded configuration.
 27. The prosthesis of claim 23 whereinthe retaining band is attached to the expandable prosthesis.
 28. Aconstrained prosthesis comprising: a prosthesis expandable from areduced diameter configuration to a fully expanded configuration, theprosthesis having an outer surface and an inner surface,; a plurality ofprosthesis retaining bands disposed about the prosthesis, each retainingband having an inner surface and an outer surface, the inner surface ofthe band disposed against the outer surface of the prosthesis, theprosthesis retaining bands maintaining the prosthesis in the reduceddiameter configuration.
 29. The constrained prosthesis of claim 28wherein the prosthesis retaining bands are made of a water solublematerial.
 30. The constrained prosthesis of claim 28, the prosthesishaving a proximal portion, a distal portion and a medial portiondisposed between the proximal portion and the distal portion and theplurality of prosthesis retaining bands including a proximal retainingband disposed about the proximal portion of the prosthesis, a distalretaining band disposed about the distal portion of the prosthesis and amedial retaining band disposed about the medial portion of theprosthesis, wherein the medial retaining band is constructed andarranged to release sooner than the proximal and distal retaining bandsin a bodily vessel.
 31. The constrained prosthesis of claim 30 whereinthe medial retaining band is made of a composition of lower molecularweight the proximal and distal retaining bands.
 32. The constrainedprosthesis of claim 30 wherein the medial retaining band is thinner thanthe proximal retaining band and the distal retaining band.
 33. Theconstrained prosthesis of claim 30 wherein the density of perforationsin the medial retaining band exceeds the density of perforations in theproximal retaining band and in the distal retaining band.
 34. Theconstrained prosthesis of claim 28, the prosthesis having a proximalportion, a distal portion and a medial portion disposed between theproximal portion and the distal portion and the plurality of prosthesisretaining bands including a proximal retaining band disposed about theproximal portion of the prosthesis, a distal retaining band disposedabout the distal portion of the prosthesis and a medial retaining banddisposed about the medial portion of the prosthesis, wherein at leastone of the proximal and distal retaining bands is constructed andarranged to release sooner than the medial retaining and in a bodilyvessel.
 35. The constrained prosthesis of claim 28, wherein at leastsome of the retaining band are constructed and arranged to releasesooner than other of the retaining bands.